In modern control systems, actuators (magnetic valves, electric motors, et cetera) are driven by means of drive signals via an output stage comprising integrated circuit loops or discrete components. The drive signals are generated by computer units. An example for driving a magnetic valve for fuel injection in internal combustion engines is disclosed in U.S. Pat. No. 5,829,412. Here, a drive signal is generated by a microcomputer. This drive signal determines the switch-on time of the magnetic valve. The drive signal is converted in a downstream component (called the angle clock) into a drive signal which is supplied to the magnetic valve output stage. The angle clock has the task to convert the drive signal, which is pregiven on a time basis or angle basis, while considering the actual crankshaft angle. The drive signal is then supplied to an output stage which undertakes the actuation of the magnetic valve by supplying current. In this way, a plurality of additional elements are disposed between the output of the drive signal quantity by the computer element and the actual supplying of current to the magnetic valve. These additional elements, especially in the case of a fault, can falsify the conversion of the drive signal quantity. Accordingly, there is a need to monitor this path.
In a corresponding manner, this applies also to other applications wherein additional electronic components are disposed between the output of the drive signal quantity, which is computed by the microcomputer, and the actual supply of current to the actuator. These additional electronic components influence the drive signal quantity.
U.S. Pat. No. 4,580,220 discloses a safety emergency arrangement for the idle operation of motor vehicles. Here, a pulsewidth-modulated drive signal is outputted by a microcomputer to drive an idle actuator. The converted drive signal quantity is detected at the terminals of the electric motor of this actuator and is read back into the microcomputer. The microcomputer then monitors the correct operation of the circuit elements lying between the microcomputer and the electric motor based on a comparison of the outputted signal quantity to the fed-back signal quantity. This analog solution requires a high complexity with respect to circuitry which contains additional sources of fault.